1. Field of the Invention
The invention relates to automated systems which include a supply circuit having hardwired loads and, more particularly, to an electrical system having at least one current-consuming load that is protected by a protective device, where a tripping parameter, i.e., a tripping current, of the protective device can be set. The invention also relates to a method for operating the electrical system.
2. Description of the Related Art
Typically, automation systems are production systems, process engineering systems or other industrially or commercially usable large-scale installations. Due to different requirements, systems of this kind are very rarely implemented in an identical design. Consequently, each system comprises different numbers and different sizes of loads. In order to avoid the outage of an entire system and, consequently, for example, interruptions to production in the event of a fault in a single load, each of the loads must be protected by a protective device, such as a cutout or circuit breaker.
Normally, a plurality of electrical loads of a system are combined into groups, with each group being protected against overloads or short-circuit by a protective device. Here, the groups are chosen such that the shutdown of one group does not inevitably lead to the total outage of the entire system. The protection for the loads or load groups is usually specified by a project engineer and subsequently installed or set by a technician. In conventional systems, adjustable protective devices are mainly used in these situations so as to allow adjustments to the tripping current to be performed as late as during an initial startup phase. The reason for this resides in the fact that the actual current consumption of the loads or load groups can only be determined to an inadequate degree during the project engineering and configuration phase. For example, individual control parameters are often not specified until after assembly and installation of the system have been completed, with the result that it is not clear in the preliminary phase which loads, such as solenoid valves, servomotors or contactor coils, will actually be in a switched-on state simultaneously during live operation.
During an initial startup, it is primarily underdimensioned protective devices that are correctively adjusted. In contrast, too highly dimensioned protective devices, in contrast, generally go unnoticed because not every operating state of every individual load or every individual load group can be taken into consideration, and because of the actual current consumption is measured during an initial startup. Selective tripping of individual protective devices is no longer ensured because in the event of a short-circuit or an overload it is sometimes no longer the too highly dimensioned, protective device disposed directly upstream of the affected load which trips, but a pre-fuse. As a result, major parts of the system are disconnected from power unnecessarily. In the worst case, the capacity of a power source (e.g., 24V control voltage) can be exceeded due to the short-circuit current, resulting in a failure of the entire system.
In addition to the absence of the protective function, it should also be taken into account that too highly dimensioned protective devices do not allow loads to be monitored. Loads may already be in a partially defective state without the corresponding protective device being tripped. In a partially defective state, sensors can record or transmit false signals or actuators can fail to perform control functions completely (e.g., a valve will not be fully closed). A protective device will trip only if there is a significant increase in current as a result of a total failure of the load.